Delay locked loops (DLL) reside in many integrated circuits for delaying an external signal to obtain an internal signal synchronized with the external signal. The internal signal usually serves as a reference signal for the integrated circuits instead of the external signal because the internal signal matches internal operating conditions of the integrated circuits, such as process, voltage, and temperature, better than the external signal does.
A typical DLL uses a delay line to delay the external signal. In most cases, the external and internal signals are initially not synchronized. The DLL performs a synchronization process to synchronize the external and internal signals. In the process, the DLL compares the external and internal signals to detect for a time delay between them. After the comparison, the DLL adjusts the delay of the delay line by a preset amount of delay to correct the time delay. After the adjustment, the DLL compares the external and internal signals again then adjusts the delay with the preset amount to correct any subsequent time delay.
The typical DLL usually repeats the comparison and adjustment many times to gradually reduce the time delay until the external and internal signals become synchronized. Repeating the comparison and adjustment many times to synchronize the external and internal signals wastes time and power.